1. Field of the Invention
The present invention relates generally to material processing, and more specifically to grinding technologies. Even more specifically, the present invention relates to surface and edge grinding technologies.
2. Discussion of the Related Art
The use of the semiconductor devices in today's commercial goods is undergoing dramatic growth. In order to expand the use of semiconductor devices in lower cost traditional products, semiconductor devices must be produced at previously unattainable low cost and with smaller size active devices and smaller line widths. Virtually every step of semiconductor device production is undergoing extensive investigation in an effort to obtain efficiencies and cost savings that will expand the market for semiconductor products.
Among the newer methods is the use of “Silicon on Insulator” and other bonding techniques where multiple silicon or other materials are bonded together then thinned to achieve desired performance. Such techniques increase efficiency of operation, lower the cost of semiconductor devices and also enable further progress in state of the art technologies.
It is generally recognized that substantial cost savings can be employed if large-scale manufacturing techniques can be brought to bear on whole wafers containing multiple, usually identical electronic devices which are simultaneously formed on the wafer substrate, prior to the wafer being divided into individual units or dies.
It has been found efficient in constructing semiconductor wafers that a substrate of semiconductor material, for example, silicon, receives overlying layers of active devices and inter-layer interconnects. After each layer is formed on the substrate, the front or active surface of the wafer is planarized or flattened so that succeeding layers are formed with a desired registry and upright orientation.
Exceedingly stringent flatness requirements are necessary for small-dimensioned patterning. As the layers are built up, one upon the other, a variety of electronic devices are formed on the wafer substrate and typically multiple, identical devices are simultaneously formed in the layer-by-layer operations. Usually, only the active or front side of the wafer undergoes extensive flattening, with the reverse or backside remaining free of layering processes and the need for precision flattening steps.
However, for larger wafers, such as the 300 mm diameter size now growing in popularity, extremely demanding flatness and surface finishing is required for both sides of the wafers. As will be appreciated, the techniques used for layer fabrication and the flattening processes cause stress inducing forces to be stored within the wafer construction. Gross chemical and atomic-level forces also are imparted to the internal structure of the semiconductor wafer and contribute to its loss of mechanical ruggedness.
Semiconductor wafers have been increasing in size in recent years in order to achieve efficiencies and cost reductions in manufacture. While most devices wafers are 6″ in diameter, a large fraction are now 8″, and the industry is tooling up for 12″ diameter wafers. These larger wafers take up much floor space and require large and heavy equipment that sometimes cannot be placed on upper floors of fabrication facilities. So for 12″ processing there is great benefit from more compact grinding equipment.
A process of bonding multiple wafers together is a newer method to fabricate these semiconductor devices. These bonded wafers require new surface finishing techniques to achieve the required flatness and surface finishes. After completing final fabrication of the multiple devices on the bonded wafers, the second wafer is then thinned from the backside to achieve the required final thickness. This is generally achieved with commercial wafer back grinders such as provided by Strasbaugh, Disco or by G&N. Such commercial grinders are typically two-step grinding with the first step done on a first rotating spindle by a coarse grind abrasive wheel, and the second step done on a separate grind spindle with a fine grind abrasive. The work piece is typically held and rotated on a chuck that retains the wafer by vacuum in a secure and flat or near flat configuration. The relative motion between the rotating grind wheel and the rotating work piece and the force provided between the two creates the energy needed to suitably grind the surfaces.